For over 90 years, annuli between an oil and gas well casing and the surrounding borehole have been cemented to prevent vertical communication of formation fluids inside the borehole. Particular difficulties have occurred in cementing wellbores when the wellbore penetrates salt or potash formations. Cement slurries that are not salt saturated have been known dissolve a portion of the formation as the cement slurry sets leaving voids and poor bonding between the cement and the salt formation. Salt saturated water has therefore been used in the preparation of cement slurries for cementing within salt formations such as sodium chloride and potassium carbonate formations. Salts generally retard setting of Portland type cements, and reduce the effectiveness of many common cement additives for Portland cement slurries. The set cements also do not have as high of a compressive strength as Portland cements prepared from fresh water. Additional setting accelerators and additives have therefore been required that increase the cost of such cements. Such salt water Portland cement slurries are therefore relatively expensive. Such salt water Portland cement slurries can also be difficult to formulate due to interactions between the salt and the many cement additives required.
Even when a salt saturated cement slurry is not required, salt water is often convenient to use. In such cases, it may be desirable to have a cement composition that can be prepared using salt water such as sea water or brine. Further, economical high strength cement slurries and cured cement compositions have a multitude of utilities such as construction and road paving.
It is therefore an object of this invention to provide an salt water cement slurry and a cured cement having a high compressive strength.
It is a further object of this invention to provide a blast furnace slag based cement with superior strength.
It is a further object of this invention to provide such a cement slurry and cured cement that can be prepared from drilling fluids in a preferred embodiment.